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Welding processes may be classified using various methods, such as processes that use pressure and those which do not, but may also be classified as fusion, solid phase, or brazing as below:

1)

Fusion Welding Processes.

(Thus this would thus include the resistance spot welding process within this group)

2)

Solid Phase/State Welding Processes.

(Thus this would thus include the flash butt welding process within this group)

3)

Brazing/Bronze Welding.

The 4 main requirements of any

Fusion Welding Process

Protection: To prevent ingress of atmospheric gases into the heating media zone and protect weld metal from oxidation both during transfer and solidification Cleaning: Of the weld metal to remove oxides and impurities, and refine the grains Adequate Adding alloying elements to the weld, to produce the desired mechanical, properties: physical or chemical properties

Heating: Of high enough intensity to cause melting of base metals and filler metals

Cleaning

Adequate

properties

Heating

Protection

To make sound

welds, we need

Welding Inspection of Steels Rev 30-03-12

Section 09 Introduction to Welding Processes Tony Whitaker Principal Lecturer TWI Middle East

9.2

Protection:

Of the heat source and weld area from oxidation

In MMA welding, the gas shield is produced from the combustion of compounds in the

electrode coating. The gas produced is mainly CO2 but electrodes are available that

produce varying amounts of hydrogen gas, which gives higher levels of penetration.

In Submerged Arc welding the gas shield is again produced from the combustion of

compounds, but these compounds are supplied in a granulated flux, which is supplied separately to the wire. MMA electrodes or SAW fluxes containing high levels of basic (calcium) compounds are used where either hydrogen control, or high toughness and strength has been specified as most basic agents have a very good cleaning effect.

In MIG/MAG & TIG welding the gas is supplied directly from a cylinder, or bulk feed

system and may be stored in a gaseous or liquid state. In TIG & MIG welding inert gases argon or helium are used while in MAG welding CO2or mixtures of CO2or O2in argon.

Cleaning:

Of surface contaminants & refinement of weld metal

The cleaning, refining and de-oxidation of the weld metal is a major requirement of all common fusion welding processes. As a weld can be considered as a casting, it is possible to use low quality wires in some processes, and yet produce high quality weld metal by adding cleaning agents to the flux. This is especially true in MMA welding, where many cleaning agents and de-oxidants may be added directly to the electrode coating. De-oxidants and cleaning agents are also generally added to FCAW & SAW fluxes. For MIG/MAG & TIG welding wires, de-oxidants, such as silicon, aluminium and manganese must be added to the wire during initial casting. Electrodes and wires for MIG & TIG welding must also be refined to the highest quality prior to casting, as they have no flux to add cleaning agents to the solidifying weld metal.

Properties:

Of sufficient values, produced through alloying

As with de-oxidants, we may add alloying elements to the weld metal via a flux in some processes to produce the desired weld metal properties. It is the main reason why there is a wide range of consumables for the MMA process. The chemical composition of the deposited weld metal can be changed easily during manufacture of the flux coating. This also increases the electrode efficiency. (Electrodes of > 160% are not uncommon for surfacing applications). In SAW, compounds such as Ferro-manganese are added to agglomerated fluxes. It is much cheaper to add alloying elements to the weld via the flux as an ore, or compound. As with the cleaning requirement described above, wires for MIG/MAG & TIG must be drawn as cast, thus all the elements required in the deposited weld metal composition must be within the cast and drawn wire and is the main reason why the range of these consumables is very limited. With the developments of flux core wires, the range of consumables for FCAW is now more extensive, as alloying elements may be easily added to the flux core in the same way as MMA electrodes fluxes.

Welding Inspection of Steels Rev 30-03-12

Section 09 Introduction to Welding Processes Tony Whitaker Principal Lecturer TWI Middle East

9.3

Heating:

Sufficiently high for the type of welding being done

There are many heat sources used for welding. In fusion welding, the main requirement of any fusion welding process is that the heat source must be of sufficient temperature to melt the materials being welded.

The intensity of this heat is also a major factor, which will mainly affect the speed of the welding operation. This section briefly describes some of the various types of fusion and solid phase welding processes available to the Welding Engineer.

In BS EN 4063 Welding/Cutting Processes are classified, or grouped as follows

The common group of welding processes are shown above as categorised in BS EN 4063 Some of the more common specific processes that fall within these groups are explained further within this section.

These main groups are divided into subsections of smaller groups relying on the same method of heating, which may themselves have sub divisions i.e.

The most common group used for welding of plate/pipe materials uses the electric arc as the main heating method. This is mainly due to portability and relative ease of electrical power generation or the use of using readily available electrical power supplies with some added equipment, which in its most basic adaptation of the arc process as Manual Metal Arc Welding may be as simple as a transformer/rectifier, 2 x high duty cycle electrical copper leads, an electrode holder, a power return clamp, a consumable electrode, and a suitably shaded visor.